This invention relates to a room air conditioner, and more particularly to a room air conditioner having improved defrosting performance.
During heating operation of a room air conditioner, frost forms on the coils of the outdoor heat exchanger of the air conditioner. As this frost reduces the performance of the heat exchanger, it is conventional to periodically carry out defrosting in which refrigerant is circulated through the air conditioner in the same direction as during cooling operation. Namely, high-temperature, high-pressure gaseous refrigerant which is discharged from the compressor is passed through the outdoor heat exchanger, where it melts the frost formed on the coils thereof. When the frost has been melted, the direction of circulation of the refrigerant is reversed, and the air conditioner returns to normal heating operation.
FIG. 1 is a schematic diagram of a conventional room air conditioner of the type to which the present invention relates. During defrosting operation, as shown by the arrows, high-temperature, high-pressure gaseous refrigerant is discharged from a compressor 1 and enters an outdoor heat exchanger 4 via discharge piping 2 and a four-way valve 3. The refrigerant melts frost which is formed on the coils of the outdoor heat exchanger 4 and in the process is condensed. It then flows through a check valve 6 which is connected in parallel with an expansion device 5 for heating operation in the form of a capillary tube, through liquid-side piping 7, and an expansion device 8 for cooling operation in the form of another capillary tube which is connected in parallel with a check valve 9. In the expansion device 8, the refrigerant is reduced in pressure and then flows through an indoor heat exchanger 10, where it is partially vaporized. From the indoor heat exchanger 10, it flows through gas-side piping 11, the four-way valve 3, return piping 12, and an accumulator 13, from which the gaseous portion of the refrigerant is sucked back into the compressor 1 to complete a cycle.
During defrosting operation, the indoor heat exchanger 10 of the air conditioner serves as an evaporator. In order to prevent cold air from being blown into the room which is being heated, an unillustrated indoor blower for the indoor heat exchanger 10 is turned off during defrosting. However, because the indoor blower is turned off, very little exchange of heat takes place in the indoor heat exchanger 10, and there is little vaporization of the low-temperature, low-pressure two-phase mixture of refrigerant passing therethrough so that much of the refrigerant which passes through the indoor heat exchanger 10 remains in a liquid state and ends up accumulating in the accumulator 13. This produces a fall in the pressure on the suction side of the compressor 1 and a decrease in the mass flow rate of gaseous refrigerant through the air conditioner. With a reduced flow rate, defrosting requires a long time, during which time the room temperature may fall to uncomfortable levels.
Furthermore, as the refrigerant which is discharged from the compressor 1 is in a superheated state, there is a great amount of heat loss to the atmosphere through the connecting piping between the discharge side of the compressor 1 and the outdoor heat exchanger 4. This lost heat in no way contributes to defrosting.